Ferrite with constricted magnetic hysteresis loop



June 20, 1961 o. ECKERT ETAL 2,989,472

FERRITE WITH CONSTRICTED MAGNETIC HYSTERESIS LOOP Filed on. 16. 1956 /VV /VV VVV V VVW LVV V V L V\NWMVVVWX\ 2w Y AAM QX QA M Z VW NW VVVVVVWVWVQ VWA/VL F1 5:. i INVENTORS BY M,MV M

United States Patent 2,989,472 FERRITE WITH CONSTRICTED MAGNETIC HYSTERESIS LOOP Oskar Eckert, Lauf (Pegnitz), and Georg Zerbes, Solingen,

Germany, assignors to Steatit-Magnesia Alr'tiengesellschaft, Lauf (Pegnitz), Germany, a corporation of Ger- Filed Oct. 16, 1956, Ser. No. 616,156 Claims priority, application Germany Oct. 20, 1955 4 Claims. (Cl. 252-425) low hysteresis losses, and, in general, small residual losses.

As indicated in the above cited literature, such materials may be subjected to thermomagnetic treatment. By thermomagnetic treatment, in this connection, is meant the passing through a thermic cycle during the simultaneous presence of a magnetic longitudinal or transverse field. The concept of longitudinal or transverse field is, in this connection, to be understood as relative to the later measuring field; a longitudinal or transverse field, respectively, means that such field, during the thermomagnetic treatment, is parallel, respectively vertical, to the later measuring field. Through this type of treatment, these ferromagnetic materials display a'substantial alteration of the form of the hysteresis loop, and hence a change of the magnetic properties.

Recently it was discovered that there exist nickel-zincferrites with constricted hysteresis loop, and it was claimed that, for instance, nickel-zinc-ferrites obtain a constricted hysteresis loop by the addition of manganese oxide and cobalt oxide. In this general form, however, this claim is completely wrong; there are only very specific ferrites showing a constricted magnetic hysteresis loop which are, consequently, susceptible to thermomagnetic treatment similarly to the metals.

The invention teaches the production of such ferrites of the nickel-zinc-ferrite system which can be subjected to thermomagnetic treatment of the above type, and are distinguished from hitherto familiar ferrites by the fact that, under the same manufacturing conditions, they have constricted hysteresis loops.

In accordance with the invention, ferrites with this characteristics in the nickel-zincferrite system must have a composition of at least 50 mol percent Fe O and a small addition of cobalt oxide. The addition of cobalt oxide is suitably determined between 0.1 and 5% by weight, calculated on the total basic batch of the nickelzinc-ferrite, expressed in metallic oxides. The invention has shown that it is particularly advantageous to choose the cobalt oxide content between 0.35 and 1% by weight, calculated on the basic batch. The nickel-zinc-ferrites in question, which react strongly to the addition of cobalt oxide with a constricted loop, cover, in the three-component system Fe O -NiO-ZnO the area defined in FIG. 4 of the drawing by the pentagon A, B, C, D, E. The compositions of the corner points in percent by weight, are:

The above fern'tes may be prepared in the usual way,

ICC

either by joint or partial precipitation, from corresponding metal salt solutions, or, as is customary in ceramic arts, they may be prepared for further processing by wet milling and mixing of the respective metal oxides. After drying, the powdered mixtures thus obtained may be given the desired form either immediately by dry pressing, extruding, or similar methods, or itmay be desirable, before ceramic forming, to proceed with a calcining firing of the whole or only a part thereof preferablybetween about 750 and 1150 C. The thus obtained parts are subjected to a sintering firing, suitably between 1250 C. and 1380 0., depending on the composition. To produce the constricted hysteresis loop in ferrites, in accordance with the invention, it is necessary that the cooling takes place slowly, particularly in the temperature range between 700 C. and room temperature. The cooling speed is dependent upon the volume of the fired body. As a criterion, it may be stated that for a ring of about 46 mm. outside diameter, 34 mm. inside diameter,'and 10 mm. height, the cooling time from 700 C. to room temperature should take not less than 12 hours. If the rings are cooled rapidly, the effect of loop constriction does not occur. However, the constriction may be regained even for n'ngs cooled too rapidly, by re-heating them to a temperature of about 700 C., and cooling them slowly, as above described.

One example of the invention follows hereafter:

In a steel ball mill are ground together 412.5 g. Fe O g. NiO, 12.5 g. ZnO, 3.25 g. CoO. After 6 hours of grinding, the slip is poured through a 4900 mesh screen (4900 meshes per square cm.) into aporcelain dish, and dried. The powder, thus obtained, is pressed, according to ceramic pressing techniques, into rings having dimensions of 59 mm. outside diameter, 35.8 mm. inside diameter, and 12 mm. height, the amount of pressure applied being about 0.5 to 1 ton/cm. The ferrite pieces thus obtained are sintered in a kiln at 1335 C. for two hours, whereupon the heat is shut off. The rings are cooled to room tepreature in the kiln during a period of approximately 24 hours. The ferrite rings thus obtained are provided with 0.4 mm. copper enamelled wire with windings as primary winding, and, as secondary winding, further 200 windings with 0.2 mm. copper enamelled 'wire are applied. The oscillographic photograph of this ferrite, produced in accordance with the invention, is shown in FIG. 1. One can distinctly recognize the loop constriction of the hysteresis loop, in contrast to a ferrite of the same basic batch but without the addition of cobalt oxide (FIG. 2).

The following experiment proves that ferrites produced in accordance with the invention are susceptible to thermomagnetic treatment:

The ferrite toroid of this example, with 100 windings as a primary winding, is placed in a kiln. While heating to 600 C., and slow cooling for 12 hours to room temperature, a longitudinal magnetic field is maintained by means of the ring winding by l a. direct current, corresponding to a magnetic field strength of about 15 a.- windings/cm. If the hysteresis loop of the ferrite after this thermo-magnetic treatment is recorded in the same manner as described above, the result is analogous to that of metals when they are subjected to heat treatment in the longitudinal magnetic field; a complete change of the form of the hysteresis loop, as may be seen in FIG. 3 takes place.

In analogous manner, heat treatment in the transverse magnetic field may be carried out with corresponding effect (see the above cited book by Bozorth) The technical progress obtained with such ferrites in accordance with the invention, may be seen in the following: with thermic longitudinal magnetization, for example, ferrites with distinctly rectangular hysteresis loop may be produced which are of importance to the entire fields of electronics and for magnetic amplification for telephone and high-frequency fields; with thermic cross magnetization, ferrites of high quality and a permeability independent of field strength may be produced, which are particularly suitable for the field of telecommunication.

We claim:

1. In a process of making a ferrite body with a constricted hysteresis loop which ferrite body is susceptible to thermomagnetic treatment to change the hysteresis loop characteristics, comprising providing a milled powder mixture consisting essentially of nickel oxide, from 1 to about 16.5% by weight of zinc oxide, 0.1 to 5% by weight of cobalt oxide and at least about 71% by weight and at least 50 mol percent of ferric oxide based on the total metal oxide content of the mixture, forming the powder mixture to the shape desired, sintering the shaped product at about 1250 C. to 1380 C., and thereafter, slowly cooling the sintered body from 700 C. down to room temperature over a period of at least about 12 hours.

2. In a process of making a ferrite body with a constricted hysteresis loop which ferrite body is susceptible to thermomagnetic treatment to change the hysteresis loop characteristics, comprising providing a milled powder mixture consisting essentially of nickel oxide, from 1 to about 16.5% by weight of Zinc oxide, 0.1 to 5% by weight of cobalt oxide and at least about 71% by weight and at least mol percent of ferric oxide based on the total metal oxide content of the mixture, forming the powder mixture to the shape desired, sintering the shaped product at about 1250 C. to 1380 C., cooling the sintered product, thereafter reheating the sintered product to a temperature of about 700 C. and then slowly cooling to room temperature over a period of at least 12 hours.

3. A fired body of a ferrite of the nickel-zinc ferrite system having a constricted magnetic hysteresis loop which ferrite body is susceptible to thermomagnetic treatment to change the hysteresis loop characteristics, said ferrite containing about 0.1 to 5% by weight of cobalt oxide, 71 to 89% by weight and at least 50 mol percent of ferric oxide calculated on the total metal oxide content of the system, about '1 to 16.5% by weight of ZnO and the remainder comprising at least 1% by' weight, being NiO, said ferrite being obtained by gradually cooling the fired body from a temperature of about 700 C. down to room temperature over a period of at least 12 hours.

4. A fired ferrite body as claimed in claim 3 wherein the cobalt oxide content is between 0.35 and 1% by weight of said ferrite.

References Cited in the file of this patent UNITED STATES PATENTS 2,452,530 Snoek Oct. 26, 1948 2,636,860 Snoek et a1. Apr. 28, 1953 2,640,813 Berge June 2, 1953 2,723,239 Harvey Nov. 8, 1955 2,73 6,708 Crowley Feb. 28, 1956 FOREIGN PATENTS 154,192 Australia Nov. 17, 1953 751,623 Great Britain July 4, 1956 756,374 Great Britain Sept. 5, 1956 1,125,577 France July 12, 1956 OTHER REFERENCES R.C.A. Review, September 1950, vol, 11, No. 3, pp. 321-363.

Weil: Comptes Rendus, vol. 234, pp. 1351 and 1352 (1952).

Wijn et al.: Philips Tech. Review, vol. 16, No, 2, pp. 49-58 (August 1954).

Bozorth et al.: Physical Review, vol. 99, pp. 1788- 1798 (September 15, 1955). 

3. A FIRED BODY OF A FERRITE OF THE NICKEL-ZINC FERRITE SYSTEM HAVING A CONSTRICTED MAGNETIC HYSTERESIS LOOP WHICH FERRITE BODY IS SUSCEPTIBLE TO THERMOMAGNETIC TREATMENT TO CHANGE THE HYSTERESIS LOOP CHARACTERISTICS, SAID FERRITE CONTAINING ABOUT 0.1 TO 5% BY WEIGHT OF COBALT OXIDE, 71 TO 89% BY WEIGHT AND AT LEAST 50 MOL PERCENT OF FER- 